文献翻译-三种关于无刷电机控制器设计的解决方案

英汉互译 Three Piece Solution For Brushless Motor Controller DesignPrepared by Kim Gauen and Jade AlberkrackUntil recently, motor control designers who wished to take advantage of the brushless DC motors unique attributes were faced with a difficult task. There were no control Ics designed to decode data coming from Hall effect sensors, let alone perform all the ancillary functions such as forward/reverse selection, overcurrent shutdown,undervoltage lockout, overtemperature shutdown, and so forth. Using discrete components to include these functions was an alternative, but discretes often consumed far too much circuit board area, especially if the control unit was to be placed inside the motor housing. Figure 1. Construction and Diagram of the MPM3003, a Three Phase Bridge That is Ideal for Driving Small Brushless DC MotorsAnother problem area was the inadequate performance of the available power transistors. Power bipolars werent favored because they cant be driven directly from a control IC, and Darlingtons have on-state voltages that are sometimes too high. Power MOSFETs seemed to be the ideal choice since they are easy to drive, efficient and inexpensive. However, designers were sometimes troubled by their inability to withstand stresses common in pulse width modulate motor controllers.THE POWER STAGEThree recently introduced devices, a power module and two linear ICs, combine to overcome the limitations of the semiconductors to form a simple design, high performance system. The power module is the MPM3003, a three phase bridge housed in a 12 pin power package (Figure 1). Its three upper transistors are 0.28 ohm P-channel power MOSFETs and the three lower devices are 0.15 ohm N-channels. All six devices have drain-to-source voltage ratings of 60V.There are three attributes that make the newer MOSFETs more rugged than their predecessors. First, they can withstand greater stress during commutations of the MOSFETs internal source drain diode. First generation MOSFETs sometimes failed when their diodes were forced through reverse recovery.(1) Second, the newer MOSFETs are less susceptible to failure caused by brief draintosource overvoltage transients. Finally, the MOSFETs in the MPM3003 have minimum gate-to-source rupture voltage ratings of 40 V instead of the industry standard 20 V. A greater rupture voltage not only improves tolerance to electrostatic discharge and unanticipated gate-to-source voltage spikes, but it also extends the lifetime of the gate oxide at all operating voltages.The MPM3003s small size and isolated package are other major benefits. Compared with mounting six TO-220s, mounting the MPM3003 is much easier and requires about half the footprint area. As shown in Figure 1, assembly begins with soldering dice to a nickel plated copper leadframe, an art well known from TO-220 manufacturing. The leadframe helps reduce thermal resistance by serving as a heat spreader. In a separate assembly, an aluminum header is covered with the dielectric, an epoxy film. To facilitate attaching the leadframe assembly to the aluminum header, the copper foil on the epoxy film is etched to form islands for the dice. Just before molding, the aluminum headers are bonded to the copper foil. Such construction gives low thermal impedance and avoids the brittleness and expense of a ceramic isolation material.Figure 2. MC33035 Representative Block DiagramTHE BRAINSThe system highlighted here is built with Motorolas MC33035 and a support chip, the MC33039. They are examples of new ICs that dramatically simplify the design of brushless motor control systems and reduce required circuit board area and parts count. Added benefits are shorter design times and improved system performance.The MC33035 is a 24-pin linear IC that can operate as the control center for a brushless DC motor control system. The main duty of the MC33035 is to decode the signals from the Hall effect sensors and generate logic for electronically commutating the motor. The commutation logic is internally fed into the six output drivers consisting of three open collector NPN transistors that drive the upper legs of the bridge and three totem pole drivers that control the devices. The open collector outputs can sink 50 mA; with some additional circuitry this allows control of either N-channel MOSFETs for higher power applications or P-channel MOSFETs if a simple interface is desired. Since the three lower totem pole outputs can source and sink 100 mA, they can drive power MOSFETs directly.FAULT MANAGEMENTThe MC33035 can detect and manage several types of faults. A common method of overcurrent detection is to tie the sources of the lower three transitors together and return them to the negative supply rail through a current sense resistor. The sense voltage, which is proportional to load current, is fed into a comparator on board the MC33035. The comparator then feeds an RS Flip-Flop, which ensures that once an overcurrent condition is detected, the output drivers turn-off the power transistors the remainder of the oscillator cycle. Without the internal flip-flop the overcurrent protection loop would rapidly cycle On and Off about the comparators threshold, causing excessive power transistor heating.In addition to overcurrent management, the MC33035 provides undervoltage lockouts that terminate the drive to the output transistors if any of three conditions occur. The first is insufficient voltage to operate the IC. The second occurs when there is insufficient voltage to drive the power MOSFET gates. Finally, the output drivers turn off the power transistors when the MC33035 does not sustain its on board 6.25 V reference. An invalid set of Hall effect signals or excessive temperature will cause shutdown, too.Whenever any fault condition is present, an NPN transistor capable of sinking 16 mA pulls the Fault Output pin low. Potential uses of the Fault Output include alerting a microprocessor of a problem, lighting an LED, implementing a soft start feature to limit motor start up currents, or latching the system off at the first sign of a problem or after a fixed delay.CONTROL FEATURESThe MC33035s circuitry contains all but one of the major elements for closed loop speed control. The only piece lacking is one that monitors motor RPM and generates a signal proportional to motor speed, a function which traditionally has been the domain of a tachometer. Once provided with a motor speed signal, the MC33035s high performance error amplifier and its internal oscillator form the last major links in the control loop.The MC33035s on-board oscillator operates at a frequency set by an external R-C. Each cycle capacitor CT (Figure 2) is charged from the reference output through resistor RT and then rapidly discharged through an internal transistor. Figure 3 shows how the resulting sawtooth-shaped waveform affects output pulse width.The MC33035 has tremendous flexibility since it works well with various Hall effect sensor spacings and the most common brushless motor windings. An MC33035 based system can easily be altered to drive motors with either delta or wye connected three phase windings with 60 or 120 degree Hall effect sensor spacing. Figure 3. The MC33035s Pulse Width Modulator Timing DiagramA companion IC, the MC33039, is a low cost, space saving alternative to a tachometer. At each positive or negative transition of the Hall effect sensors the MC33039 generates a pulse with a fixed on time. The output signal can then be filtered to obtain a voltage proportional to motor speed. Design of an MC33035/39 based system should begin with setting the system timing, which originates in the MC33039.ASSEMBLING THE PIECESSelection of timing components for the MC33039 is based on the desired maximum motor RPM. For the motor used in this application (Pittman ELCOM 5112) there are two electrical degrees for every mechanical degree since the permanent magnet on the rotor has two pairs of poles. Therefore, for every mechanical revolution each Hall effect sensor delivers two pulses and the three sensors generate six pulses. The MC33039 generates 12, one for each rising and falling edge.For a given maximum motor speed, the output pulse width has a maximum limit. If we assume a maximum desired speed of 5000 RPM, which is about 83 revolutions per second, the MC33039 will generate 83 x 12, or 1000 pulses per second. The 1 kHz frequency dictates that the maximum pulse width must be less than 1 ms. From Figure 4, which is taken from the MC33039s data sheet, one can determine that R1 and C1 values of 43 k and 22 nF result in a pulse width of 950s. To set the system PWM frequency, refer to the MC33035s data sheet. There it shows that setting R2 and C2 to 5.1 k and 0.01F gives a nominal pulse width modulation frequency of 24 kHz, just above the audible range.Both inputs and the output of the MC33035s error amplifier are accessible to accommodate various control methods. For open loop control you can feed a reference signal proportional to desired speed into the error amplifiers non-inverting input. The error amplifier is then configured as a unity gain voltage follower by connecting its inverting input to its output. The error amplifiers output is then compared to the output of the oscillator to obtain a PWM signal proportional to desired motor speed unless the control loop is overridden by an overcurrent or fault condition.For closed loop control one approach is to filter the MC33039s output with a low pass filter to generate a voltage proportional to motor speed and feed the resulting signal into the inverting input of the MC33035s comparator. A signal proportional to desired motor speed drives the non-inverting input, and the ratio of the input and feedback resistors R3 and R4 control gain. In this design, low pass filtering and generating the error signal are combined by using feedback capacitor,C3. Ideally, the integrator/error amplifier should produce a ripple free output even at low motor speeds. To do so at very low speeds reduces system response time, however. Component values must be adjusted according to the rotors and loads inertia and friction. In this particular application the values 1 Mand 0.1F (t = 100 ms) give good dynamic response and stability.When motor speed falls below the desired speed, the MC33035 extends the output pulse width to the drive transistors. When motor speed is greater than the desired speed, the duty cycle decreases. However, if the input signal abruptly demands a much lower speed, the duty cycle could fall to zero and the motor would coast to desired low speed. Therefore, since the MC33035 has no provision to dynamically brake the motor and thus control rapid deceleration, it is best suited for applications which have a large frictional load or those that do not require a controlled, abrupt deceleration. The schematic of a closed loop brushless motor control system is shown in Figure5. Shown in Figure 11 is a completed brushless motor control.Figure 4. fout Pulse Width versus Timing Resistor Figure 5. Representative Block Diagram of MC33039三种关于无刷电机控制器设计的解决方案由Kim Gauen和 Jade Alberkrack的设计近来，希望利用直流无刷电机特性的电机控制器设计者面临着一个很大的难题。没有控制信息系统的设计，它的解码数据来自霍尔效应传感器，它可以执行所有的辅助功能，例如正反转控制，过流停止，低压停止，过热关闭等许多功能。给它使用分立元件是一个可选折的办法，但是这些分立元件常常要占用很大的电路板面积，尤其是如果控制部件是被布置在电动机内部的情况下。另一个问题所在是有效功率晶体管的不够充分的性能。双极功率管不是有利的，因为它们不能被从开始控制的集成电路直接地驱动，还有用的达林顿管额定电压有时会太高。功率场效应晶体管似乎是个理想得选折，因为他们很容易被驱动，而且效率高，价格便宜。然而，设计者有时会因为它们而不能禁得住在脉冲宽度上调节电机控制器的重压而烦恼。图1.实物与MPM3003图解，一个理想的三相桥式直流无刷电机的驱动图功 率 模 块三个最近引进的设计方案，一个功率模块和两个线性集成块，共同克服半导体的限制，形成一个简单的设计，高性能系统。功率模块是MPM3003，在十二脚的功率块内部是一个三相桥式驱动电路（如图1所示）。在它上面的是三个晶体管，是0.28欧姆的P沟道功率场效应晶体管，下面的三个是0.15欧姆的N沟道功率场效应晶体管。六只晶体管的漏源极额定电压均是60伏特。他们的三个外观使新出来的场效应晶体管比原来的管子更粗糙。一、在交换场效应管内部的二极管时，他们能承受更大的电压。二、新出来的场效应管受到小的瞬时的漏源电压时所导致的失败的影响。三、在MPM3003内部的场效应晶体管有个很小的栅源极断电压40伏，代替了工业标准20伏电压。一个大的断电压不仅可以改善静电流出和没有预知的栅源极电压接地，而且还可以延长常规运行电压下的晶体管的寿命。小型MPM3003的独立包装是它另一个主要的好处。与使用六对TO-220s相比较而言，使用MPM3003要更加容易并且只要一半的板面积。如图1所示，装配是从焊接的模子开始，连接在板子上面的镀铜上，这是个来自TO-220制造业的知名技术。此设计通过散热分布器减少热变电阻值。在一个独立的装配上，用铝覆盖绝缘材料，这是个环氧薄膜。要更容易的连接板面装配到铝片上，在环氧薄膜上的铜箔形成一个又一个单独的模块。在成型之前，铝与铜箔被结合在一起。这样的设计提供了低热量阻抗并且避免了陶瓷隔离材料的易碎性并降低了它的费用。图2 MC33035的代表性结构图主 体这里主要的系统是用摩托罗拉公司的MC33035和维持芯片MC33039。他们是显著简化无刷电动机控制系统和减少必需的电路板面积和零件个数的新的集成模块的例子。增加它的好处是有了更短的设计时间和被改进的系统性能。MC33035是作为直流无刷电机控制系统控制中心的一个24脚的线性集成电路模块。MC33035的主要任务是解码霍尔效应传感器的信号和电子换向马达产生的逻辑。换向逻辑内部是六个输出驱动器，它包括桥上部分的三个NPN场效应晶体管和三个控制装置的图腾柱驱动器。开放收藏品输出可达到50安培，如果想得到一个简单的接口，用一个另外的电路，它能控制大功率应用N沟道场效应，或者P沟道场效应经晶体管。因为三个较低的图腾柱输出能产生或降低100毫安，他们能直接的输出功率场效应管。 错误的操作MC33035能查出并处理几个类型的错误。过载电流侦察的一个普通的方法是，将较低的三个晶体管的源极连在一起，通过直流感应电阻器使他们回到负电源。与过载电流成比例的感应电压，被反馈到MC33035上的比较器。比较器再供给RS双稳态多谐振荡器，它确保一旦有过载电流就被查出。输出驱动器支路功率晶体管使震荡器循环。没有内在的双稳态多谐震荡器，过电流保护回路就会在比较器的门限迅速的循环地开与关，导致过多的功率晶体管发热。除了过流管理之外，如果下面的三个情况中的任一个发生时，MC33035提供低压驱动使输出晶体管停止工作。一是用不足的电压操作集成电路。二是用不足的电压驱动功率场效应管的门极。三是，当 MC33035不能承受它的6.25伏参考电压时，输出驱动器关断功率晶体管。无效的霍尔效应信号或过高的温度也将导致门关断。当任何一个错误的情况发生时，一个降低16安培的NPN晶体管能使出错的输出脚的电压变低。对错误输出的潜在的用途包括警告问题的微处理器，点亮发光二极管，实现一个平稳启动特征来限制电动机的启动电流，或者在出现问题时与在固定延迟以后，关闭系统。控制作用MC33035的电路几乎包含适合闭环速度控制的任一个主要元素。唯一的接合不足是电机可靠性能测定监控和产生一个与电机速度成比例的信号，它的主要功能是测出转速计的转动范围。一旦拥有了电机速度信号， MC33035的高性能误差信号放大器和它的内部振荡器型式对于操纵系统维持在主要的连接。 MC33035上面的振荡器在隔开外部的R-C频率时运转起来。每个周期电容CT（如图2所示）被通过电阻RT的参考输出充满电，然后又通过内部晶体管迅速的放电。图3中显示了锯齿波对输出脉冲宽度的影响。MC33035有很大的机动性，因为它在不同的霍尔效应传感器间距和公共的无刷电机绕组，能工作的很好。一个MC33035根本系统能很容易的改变驱动电机的方向，通过三相绕组的三角形或星型连接和60度或120度的霍尔效应传感器间距来改变。图3 MC33035的脉冲宽度调节器的时间矢量图公共的集成电路MC33039，成本低，体积小供给转速计。对于每一个MC33039的霍尔效应传感器的正负转换，以一个确定的时间产生脉冲。输出信号被与电机速度成比例的电压过滤。一个MC33035/39基础体系设计应该首先安装定时系统，它在MC33039的内部工作。封 装MC33039的定时部分的选折是基于期望的最高的电机可靠性能测定。在此应用中的电动机对于每个机械度都有两个电度，因为在转子上的永久磁铁有两对电极。因此，每个旋转周各自的霍尔效应传感器产生两个脉冲，及三个传感器产生六个脉冲。MC33039产生十二个脉冲，对应于每个上升沿和下降沿。为了特定的最大的电机速度，输出脉冲宽度有最大极限。我们假设最大的理想速度为5000转，它每秒大约83转，MC33039能产生8312转，或者每秒产生1000个脉冲。1 kHz频率规定最大的脉冲宽度必须小于1毫秒。如图4，从MC33039的数据表可以看出，它可以确定43千欧姆的电阻R1和22 nF的电容C1产生一个950s的脉冲宽度。确定系统脉宽调制频率，参考MC33035的数据表。它表明了安装5.1 k的R2和0.01F的C2共给一个24 kHz的脉冲宽度频率，刚好超过规定的范围。图4.脉冲宽度与时标电阻的对应关系MC33035的误差信号放大器的输入与输出是可供给多种控制方法。对于开路控制，你可以给一个同理想转速成比例的信号到误差信号放大器的同相输入。误差信号放大器作为电压输出跟随器被设定，通过连接它的倒相输入到输出。误差信号放大器的输出就为振荡器的输出，为获得一个同理想电机转速成比例的脉宽调制信号，除非控制系统被过流或故障毁坏。闭环控制器近似于MC33039的输出滤波器，以低通过滤器产生一个与电动机转速成比例的电压。正比于理想电机转速的信号驱动同相输入，输入和反馈电阻R3、R4的比率控制增益。在此设计中，低通滤波器和误差信号的产生是被反馈电容C3所结合。理想时，误差信号放大器在低的电机转速下产生一个自由输出波动。这样，在低转速时减少了系统响应时间，然而，元件值必须能依照转子和负载的惯性和摩擦进行调整。在这个特别的应用中，1M和0.1F (t=100ms)的阻值提供了好的动态响应和稳定性。当电机转速降低到理想转速之下时，MC33035扩大输出脉冲宽度到驱动晶体管。当电机转速大于理想转速时，循环周期减少。然而，如果输入信号突然需要一个很低的转速，循环转可以降为零，电动机就会降到理想的低转速。因此，MC33035没有提供动力制动电动机，因而迅速地控制减速。这是最合适的应用软件，它有一些大的摩擦负载命令控制，会突然的减速。一个闭环直流无刷电机控制系统如图5所示。